Friday 18 February 2011

Feet of Clay

When firing a wood kiln, or salt or soda, one of the challenges is preventing the feet of the vessels from sticking to the shelves. In any of these firings the atmosphere in the kiln is full of glass making materials, either as fine particles of ash or gaseous sodium trying to flux any free silica in the clay to a liquid glaze. In fact, that is our objective, and by allowing this flow of glass making materials to wash over our vessels we invite nature to glaze and decorate our work for us. It is difficult to be selective, however, about where those gases or particles flow without sacrificing the spontaneity of the glaze effect on the whole vessel. If the liquid glass flows down to the foot of the vessel, then when it cools the foot will be stuck to the kiln shelf by solid glass. This is difficult to remove without chipping the piece or damaging the kiln shelf, and such losses can become quite expensive.

There are several ways of addressing this challenge and I employ two methods in my kiln, depending on where the pots are to be placed. The first is to try to prevent the pots from sticking. My first step in this process is to design my feet so that there is a minimum amount of surface area in contact with the kiln shelf. The foot ring itself is trimmed with a chamfer on each edge so that only a thinly angled line touches the shelf. This also creates a slight overhang to help prevent fly ash from getting under the foot. When the vessel is removed from the kiln the foot ring can be touched up with some sand paper and "Viola!", a nice smooth foot ring. When I am waxing the feet of some vessels before glazing, on plates for example, I use a special wax mixture of candle wax, kerosene and a handful of alumina powder. The wax burns off in the kiln, leaving a very fine residue of alumina between the vessel and the kiln shelf. Alumina (Al2O3) is a highly refractory material, the melting point of which is about 2040C, and so it remains as a dry powder even at glaze firing temperatures, and will serve the same purpose as flour on the work bench when you are making pastry or bread, preventing sticking. Following the same train of thought, Alumina is used as a coating on kiln shelves and kiln furniture to prevent sticking, just as flour is used on the inside of a cake tin. On its own, however, alumina floats around as a powder and can stick to glaze surfaces making them matte and unattractive, so a coating mixture containing some clay material as a fixative is necessary. The mixture which I use is Alumina 2: Kaolin 1 proportionately by weight, mixed with enough water to make is a pourable creamy consistency. I put this into a watering can and pour it over the surface of the kiln shelves, then put them out in the sun to dry. After every firing I scrape any accumulated ash or soda deposits off the kiln shelves, so that they are ready to be coated again for the next firing. It is important to use a dust mask and eye protection during this process! The materials are all non toxic, but inhaling dust can cause lung disease, and chips of broken glass in the eyes should be avoided at all costs!

My other approach to this challenge is to accept that a wood or soda firing is what it is. There is going to be ash and glass dripping of the pots, and it's going to leave marks. If you are trying to avoid that and it happens by accident it can leave nasty scars on the pots. If, however, you accept it and allow it to happen as a part of the total design, those marks become cicatrices, like tribal scars, and a beautiful expression of the firing process in the finished work.

I do not use wad mix directly on the clay, as that goes in the nasty scar basket. Instead I use a ball of fire clay, rolled in alumina, stuffed inside a sea shell. A set of three, or sometimes more, of these will form a stand on which the vessel can be placed, raising it off the kiln shelf. When the kiln is fired, the salt in the shell will volatilize off leaving flashing marks on the clay. The Calcium Carbonate (CaCO3) in the shell will lose Carbon Dioxide (CO2) and become Calcium Oxide (CaO), still retaining its original structure between the vessel and the fire clay. Any glaze, ash or soda will flow into the shell structure. When the vessel is removed from the kiln and placed in a bucket of water, the Calcium Oxide (Quick lime) will rehydrate to become Calcium Hydroxide (Ca(OH)2 or Slaked Lime), and will just wash off the vessel leaving a fossil like cicatrix where it was in contact with the surface. The slaked lime goes on the compost heap. A touch up of the sharp edges left on the glaze deposit with some sand paper, and Robert is your fathers brother! This is the method I use at the fire face, where the forces of nature are most energetic and capricious. I described this process and my feelings about it in my "Art for Eternity" entry, and I invite you to read that by all means. The greatest challenge for a potter, however, is knowing when to take control, and knowing when to surrender it. It is this balance, this dance with the elements, that creates such beauty, that gives great joy to the user of these vessels, and makes being a potter such a fulfilling career.

Friday 11 February 2011

Fire & Snow

The grey winter light filters softly through the bedroom windows as I emerge reluctantly from my warm cocoon. It is Sunday, so there is no need for Mika and the kids to surface yet. I quietly don the work clothes I put on the chair beside the bed last night, the touch of the fabric cold against my skin. I walk through the children’s room to the studio, change into my heavy work boots and step through the studio doors into the stinging cold. My boots crunch across the snowy ground as I walk to the kiln shed, the snow flakes whispering as they fall. My breath billows in clouds of vapour and forms droplets of condensation on my moustache. The clock on the shelf says 7:30 am. The pyrometer display tells me it is -16C. I hope it is wrong.

The sulphurous smell of the freshly struck match is quickly replaced by the fragrance of burning spruce as I set light to the fronds and kindling I arranged in the dual fire mouths of the kiln last night. The fire crackles as the flame climbs hungrily from twig to branch, and when it is burning well I check the top of the chimney to make sure the fire is being drawn through the kiln properly. When the first of the wood starts to crumble into embers I place five pieces of wood, cross hatched, in each fire box. Twenty minutes have passed since I lit the kiln, the pyro reads 15C. Satisfied, I return to the house to light the kitchen stove and start cooking breakfast.

The wood stove heats up quickly, warming the kitchen and living room, and the family emerges one by one. One must never waste a hot oven, especially on a cold snowy day, so I make batch of scones. Every twenty minutes I go out to stoke the kiln, and by the time the scones are cooked the kiln and the oven are both reading 180c. Scones with lashings of blueberry jam and cream, cappuccino for Mika and me, warm milk and honey for the kids. I leave the washing up to the family and go out to tend the kiln.

The snow has stopped falling, the fire in the kiln pops and crackles, the rest of the world is still and hushed. The plum trees in the garden are just beginning to bloom, and the snow decorates the blossoms with crystal mantles. The kiln gets hungrier as it heats up, rising 100C per hour, and the stokes get closer together; every ten minutes, every five..

The tribe comes rushing from the house in full winter regalia, and amid shouts, bursts of laughter and flurries of snow balls, an igloo and a giant snowman arise in the garden. Happy and exhausted, the children return to the house for lunch. The kiln has reached 6ooC, and I begin to stoke on top of the fire grates. Now the firing starts to get busy, climbing three hundred degrees in half an hour. 700... 800... 900C, I adjust the damper and the kiln starts to reduce. Mika sends Sora out with a lunch tray. "Buta-don", simmered pork on rice, with vegetables and miso soup. We drink green tea from Yunomi Chawan as we talk.

The tea is hot, 85C, when it is poured into the Yunomi, and the porcelaineous clay holds the heat well. In the west, we fill our cups with tea or coffee and they are too hot to hold, which is why we invented handles. In Japan, however, a yunomi is used. "Yunomi Chawan" (湯呑茶碗) means "Tea Bowl for Hot Water", and yet it has no handle. It is not used the same way as a "Macha Chawan" (抹茶茶碗), which is for powdered green tea in the tea ceremony. Instead, it is filled from a small tea pot to two thirds, which leaves the top third cool enough to lift between the index finger and thumb. Once lifted, it's foot is rested on the upturned fingers of the left hand, and it is lifted to the lips with both hands.

The Yunomi in this firing are designed with a change of direction at the two third mark, with a concave curve up to the rim which makes it easy to pick up with one hand. The foot is quite high, which protects the hand from the hot hip of the pot, and it's diameter is just nice to fit between the first and third joints of your fingers. Of course, people have different sized hands, and generally men's hands are larger than women's, so two sizes are made. They are called "Me-Oto" (夫婦), which means husband and wife, but the difference in size is for practical purposes, not social discrimination.

Sora sits with me as I fire the kiln, and we talk of many things. I explain to her about the trees using sunlight as energy to split the carbon dioxide in the air into carbon, which becomes the wood, and free oxygen which we need to breath. How, when I burn the wood, the flame releases the carbon and recombines it with oxygen to create energy and heat. How the hot, free carbon flows hungrily through the kiln, dragging oxygen from the materials in the clay, reducing them and changing their structure and colour. How everything in the universe is made of the same atoms, constantly combining, separating and recombining to become all the things around us, and that we are a part of that. That everything that is, always was, and always will be, it is merely changing form throughout eternity.

She is quiet for a while, as the heat of the kiln climbs and flames come blasting from the blow hole at the top of the door, like dragons tongues licking from the depths of the kiln.

"Dad," she says quietly, "What is Death?"

I look at her. "What do you think it is?" I ask.

"I don't know, really, that's why I'm asking you."

"Well," I say, smiling, "I think it's important to think about what life is first. Our bodies and all the atoms in them follow the same rules as the rest of the universe, so when we die, they change and become other things. Our spirit, our self, exists as surely as our bodies, does it not? The you that looks out through your eyes and sees the world and calls it beautiful is as real as the eyes that it looks through, but it cannot be measured. Yet it is, as much and no less as everything else that is, so how can it ever cease to be, if nothing else in the universe does?"

She nods slowly, a look of consideration on her face. The wind picks up and snow begins to fall once more. A flurry of snow flakes swirls into the kiln shed and a single flake sticks briefly to her cheek, before melting and running down to her chin like a tear drop.

I reach out and gently wipe it away. "I believe," I say,"That there is a great and universal spirit that pervades the universe, though we cannot see it nor measure it. It is like water, amorphous and all pervading. But in special circumstances, it crystallises into individual souls, like snow flakes. Every one is different, individual, special, and through all eternity it will never be repeated. For it's brief time it is the most beautiful and perfect crystallisation of the universal spirit, and though it may be surrounded by overwhelming numbers of other flakes, lost in drifts, buffeted by storms, and feels cold and alone sometimes, it partakes of the essence that is life itself and it is never really alone. And when its time is done, it will melt and return to the water from which it came, and flow once again as part of the universal spirit. It may, one day, be part of another snow flake, but the stuff of which it is made has always been and will never not be."

I hug her as the wind begins to buffet the kiln shed. "I believe that death is no more than the melting of a snow flake and it's return to the water from which it came. It is nothing to fear. What is much more important is to revel in the beauty and wonder of that snow flake, for it is unique and the miracle of its existence makes the universe a richer and more beautiful place."

She smiles at me. "Thank you, Dad. I love you."

"I love you, too." I say. "It's getting too cold out here, you'd better go inside."

The firing continues through the dusk and into the dark. Inside the kiln, as the temperature rises to 1300C, the minerals in the wood ash flying with the flames through the kiln melt into glass, and the yunomi change, vitrify, and become something new. When I open the kiln I will discover beauty that I have not made, that I have not seen before, but which has been born of the forces of nature, each vessel a new and individual expression of the beauty of nature. I feed the kiln, I listen to it and watch the flame, and I wait.

The cones are down, I believe the firing is done. I wait for it to cool to 1100C before stoking one last bundle of wood in each fire mouth and sealing the kiln. The snow has gone, the sky is clear, a crescent moon smiles down at me and the world shines in the darkness. The snow creaks beneath my feet as I go home for my supper, home in the warmth of my families embrace.

I have never really been a "chronicler" by nature. I find that I now have a lot of experiences, and things that I have learned from them, which I would like to share; And people like you seem to find them of value, which is very encouraging. Thank you.

The experiences go on though, every day, and I find myself with the conundrum of having a lot to write about and no time to write it! No words will ever compare to the actual feel of snow flakes on your skin, the smooth texture of a warm yunomi in your hand, the flavour and fragrance of green tea or the sound of children's laughter in the whispering snow.